Electron tube



'May 193.7. 4 I J. RICHTER ET A; ,Q

' ELECTRON ,fUBE

Fi led Aug. 19, 19:55

7 INVENTORS WOLFGANG FEDEF-MANN JOHANNES RICHTER, OTTO SCHEI VEFM BY F n" scuhsrtn- A ORNEY 5 'tion of positive half-waves-oi' cycles of the modu- Patented May 4, 1937 UNITED STATES 2.979.085 ELECTRON ms Johannes Richter, Otto Schrlever, Fritz Schriiter',

and Wolfgang Federmann,

Berlin, Germany,

assignors to Telefunken Gesellsoliaft fiir v .Drahtlose Telegraphic -m. b. 11., Berlin, Germany, a corpo ation of Germany ny August 19, 1932 Appl cant August 19, 1933, Serial No. 685,90l l 4 Claims. (Cl. 2511-27) This invention relates to and is concerned with a method of modulating and means to modulate the intensity of electron beams or pencils. It is especially adapted to be used in connection with cathode ray or Braun. tubes and most particularly 1 so where these tubes are employed for television. work.

Modulation by theimpulses correspondingto brightness variations to be reproduced may be efl'ected by magnetic or electrical means. In modulations of this kind it is discovered that the punctiform focusing of the pencil of electron rays accomplished by various ways and means depends upon the modulation, especially when such modulation is brought about by influencing the volume of electrons accessible to the plate or anode potential.

Modulations of this kind are often eflected by alternating potentials impressed upon a distinct control electrode, the latter and its function being taken over by an electrode serving for the concentration of the electrons and operated with a constant negative biasing potential, for example, by a Wehnelt cylinder or a surface electrode mounted-in the vicinity of the cathode. Under the action of the modulating potential at the control element, the diameter of the electron-ray pencil is altered and thus also the size of the spot thrown upon the fluorescent screen, as is understood by those skilled in the art. This resulting disturbingeflect of the modulation upon the oathode ray pencil may be counteracted and neutralized by the additional provision of a magnetic field, for instance, in the form of an annular coil.

It has been further shown that in such modulations, especially in the case of tubes in which the constrictive forces of agaseous atmosphere are utilized cooperatively for the purpose of in-* 'suring concentration or focusing actions, it may 40. occur that in spite of such supplemental focusing by 'a magnetic field the penciledcathode rays fail to preserve a reduced pencil diameter such as required, but that the pencilbecomes spread and blurred with the result .that, upon the whole, 45 it assumes a larger inexactly contoured diameter.

Experiments have shown that this phenomenon is ascribable to the circumstance that, in the modulation, alternating potentials are impressed upon the control means, whereby due to the aclating impulses more electrons are released thanv the constant negative control potential admits, and the negative half-waves may produce the effect that the value of the biasing voltage cor- 55 responding to the minimum current intensity of the pencil is not attained. In such instancesthe flow of electrons towards the anode is'then completely impeded with the result that pencil-focusing ions-are not formed, and such ions as may 60 exist are conveyed by the prevailing high voltage to the control electrode. What has thus happened is'that the pencil space-charge has beendestroyed and must be restored or re-formed by the flow or stream of electrons resumed during the next positive half-cycle. It thus happens that the whole impression of a picture re-created by alternating" current modulated pencils is blurred.

Now, in order to obviate this inconvenience only rectified modulating impulses, according to'the present invention, influence the electron pencil with the result that interruptions in the flow of electrons caused by high negative potentials .will no longer occur. In practicing this invention it is not possible to utilize a rectifier eflect set up at the control electrodes inside the discharge tube proper, indeed, the modulation impulses used for control actions must be furnished from a distinct rectifier device, although this may be accomplished inside or outsidethe tube.

The basic idea of the invention is capable oi being incorporated in a number of different circuit schemes.

Fig. 1 illustrates a general circuit arrangement in which K denotes the cathode, A the anode, and Z a Wehnelt focusing or a control cylinder. P designates a pair of deflector plates and S is the auxiliary coil designed to maintain the focusing.

The Wehnelt cylinder Z has a biasing voltage impressed upon it from a battery B, whereas across the resistance W modulation impulses are supplied from the scource M. If desired, the said impulses may be superimposed upon a carrier frequency. N is a conducting coating on the interior wall of the tube envelope.

Now, according to the invention the modulation impulses coming from M are rectified before they are impressed 'upon across the resistance W. With this end in view, as shown at Fig. 2, an amplifying detector R may be connected between M and W. 0 is a conducting coating on the outside of the tube.

Fig. 3 illustrates another embodiment of the idea underlying this invention. In this scheme, the modulation impulses are fed in by way of a valve V, the latter consisting, for example, of a triode tube in which gridand plate arejoined.

Fig. 4'finally shows a circuit arrangement in i which one half-cycle of the modulation voltage is suppressed by the short-circuitlng action of a tube VI. 7

If the modulating impulses are supplied by means of a carrier wave the latter may be eliminated during rectification or else by distinct means such as filter circuits and the like. A- rectifying discharge path could also: be included within the Braun tube, this path doing no cooper'ative work in the formation of focusing of the pencil, serving merely to furnish rectified control impulses to the control element.

As above explained provision has been made to effect the intensity modulation of electron pen oils 0 v beams, especially those serving for the recreation of television pictures only in such a way that in the electric or magnetic control means only rectified impulses are caused to act upon the pencil. By the aid of such-a method it is quite readily feasible to effectively reproduce intensity.

, ing and curving.

. By the adoption of "a certain construction principle in the tube this disturbing action can be eliminated according to the invention. For example, if the discharge tube is interiorly rendered conductive throughout or only at the places or in the regions tending to become charged, it is discovered that the inclination on the part of picture lines to arcuate paths will be caused to disappear. The presence of parts of conductors' which tend to surround the pencil uniformly or nearly so has the result that charges upon the glass wall which would normally exercise a unilateral efiect, are caused to become uniformly distributed around the pencil with the result that unilateral deflection will be precluded. According to this invention, the said conducting parts designed to insure wall charge actionaare related electrically to the electrodes of the tube so far as the potentials-are. concerned in 'order that they may not impair or impede the passage of the pencil as a result of their potentials or the potential surfaces occasioned by their charge.

Extremely sharp picture re-creation is obtainable also by "providing the tube exteriorly with conducting coats, and by maintaining these external conducting portions, for instance, at anode potential. Also outside conductors have the effect that whatever charges may be present, for instance, upon the insulating glass wall, will be distributed in a roughly uniform manner upon the same so that the eifect thereof manifestingitself in causing curving of the lines modulated by rectified impulses 'issubstantially lessened.

Having thus described our invention, we claim: 1. A system for controlling an electron beam which comprisesua gas filled cathode ray tube having a source of electrons, an anode, a concentrating electrode and a screen upon which the electron beam developed by. the application of suitable voltages to the said electrodes causes luminous effects, means for applying to the concentrating electrode a negative biasingvoltage. means for developing a constant magnetic field to supplement the concentrating action of the focusing electrode and also the gaseous atmosphere upon the developed electron beam, a rectifier device to which modulation signals are supplied, and

means for superimposingthe rectified output" trode.

from said rectifier upon the normal negative biasing voltage applied to the concentrating electrode.

2. A system for controlling an electron beam which comprises a gas filled cathode ray tube having a source of electrons, an anode, a concentrating electrode and a screen upon which the electron beam developed by the application of suitable voltages appliedQbetween the electron source and the anode causes luminous effects, a

conductive coating deposited on the exterior of the tube envelope surrounding the electron path through the tube for a substantial portion of the tube length, means for applying to the beam concentrating electrode a negative biasing voltage, means for developing a constant magnetic field to supplement the focusing action of the concentrating electrode, means for maintaining the conductive coating at a potential relative to the electron source of the same order as that of the anode electrode, a rectifier device to which modulation signals are supplied, and means for superimposing the rectified output from said rectifier upon the normal negative biasing voltage applied to the concentrating electrode.

3. A system for controlling an electron beam which comprises a gas filled cathode ray tube having a source of electrons, an anode, a concentrating electrode and a screen upon which the electron beam developed by the application of suitable voltages applied between the electron source and the anode causes luminous effects, a

conductive coating deposited on the interior wall of the tube envelope and biased with respect to the cathode, said coating surrounding the electron path through the tube for a substantial portion of the'tube length, means for applying to the beam concentrating electrode a negative biasing voltage, means for developing a constant magnetic field to supplement the focusing action of. the concentrating electrode, a rectifier device 'to which modulation signals are supplied, and

means for superimposing the rectified output from said rectifier upon the normal negative biasing voltage applied to the concentrating electrode.

4. A system for controlling an electron beam which comprises a gas filled cathode ray tube having a source of electrons, an anode, a

concentrating electrode and a screen upon which the electron beam developed by the application of suitable voltages to the said electrodes causes .luminous effects, means for applying to the concentrating electrode a negative biasing voltag means for developing a constant magnetic fie d to supplement the focusing action of the concentrating electrode and also the gaseous atmosphere upon the developed electron beam, 9. conductive coating adapted to be biased with respect to the cathode of the gas filled tube,,said coating being deposited-on the tube envelope, a rectifier device to which modulation signals are supplied;

and means for superimposing the rectified output from said rectifier upon the normal negative biasing voltage applied to the concentrating elec- JOHANNES RICHTER. o'rro scrmmvrza.

FRITZ scnao'rna. WOLFGANG FEDERMANN. 

